Expansive additive for lime cement and process for the preparation of the same

ABSTRACT

An expansive additive composition for use in controlling the expansion of cement on aging comprising a sintered mixture of lime and at least one additive selected from the group consisting of ferric oxide, calcium fluoride and calcium sulfate is disclosed. The process for preparing the expansive additive composition is also disclosed.

AU 116 EX United States Patent [1 1 Ogura et al.

[451 Apr. 2, 1974 EXPANSlVE ADDlTlVE FOR LIME CEMENT AND PROCESS FOR THEPREPARATION OF THE SAME [75] Inventors: Hirokatsu Ogura; TatsuoTakizawa,

both of Tokyo; Yoshizo Ono; Yukuo Taketsume, both of Niigata, all ofJapan [73] Assignee: Denki Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan[22] Filed: Aug. 6, 1971 [21] Appl. No.: 169,811

Related US. Application Data [58] Field of Search 106/89, 97, I02, 314,315

[56] References Cited UNITED STATES PATENTS 1,997,782 4/1935 Windecker106/102 3,232,778 2/1966 Dean 106/97 3,251,701 5/1966 Klein 106/89Primary Examiner-James E. Poer Attorney, Agent, or FirmSughrue,Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT An expansive additivecomposition for use in controlling the expansion of cement onaging-comprising a sintered rni xtu.r.e of lime and at least oneadditive selected from the group consisting of ferric oxide, ga-

cium fluoride and calcium sulfate is disclosed. The -T rocess forpreparing the expansive additive composition is also disclosed.

4 Claims, 3 Drawing Figures EXPANSIVE ADDITIVE FOR LIME CEMENT ANDPROCESS FOR THE PREPARATION OF THE SAME CROSS REFERENCE TO RELATEDAPPLICATIONS BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to an expansive additive for lime systemcements and to a process for preparing an expansive additive for limesystem cements. More particularly, this invention relates to a processfor preparing an expansive additive for lime system cements by adding tolime at least one of the ferric oxides, calcium fluoride, and calciumsulfate and sintering or melting the mixture.

2. Description of the Prior Art A cement containing free lime or calciumoxide frequently expands during the setting and hardening thereof.Hence, such a cement has hitherto been considered to be undesirablesince the expansion causes a lack of stability in quality.

On the other hand, however, were it possible to control the expansioncharacteristics of such a cement so that the expansion of the cementoccurred at a proper period after hardening of the cement, it might bequite preferable. In the case of compounding ordinary calcium oxideprepared by sintering limestone at a temperature of about 1,200C to1,400C in a cement, it expands rapidly immediately after setting. Hence,such a cement cannot be used practically.

Investigations of a sintering process for lime, capable of maintaining amild expansion characteristic of the cement up to a suitable time afterhardening of the cement by improving the rapid expansion of the freelime, resulted in the discovery of the process of this inventron.

SUMMARY OF THE INVENTION The present invention is a process for thepreparation of an expansive additive for lime system cement whichcomprises adding at least one member selected from the group consistingof ferric oxide Fe,o, calcium fluoride (CaF and calcium sulfate (CaSO tolime, crushing the mixture, and sintering or melting the mixture at atemperature at which the additive or additives are not decomposed.

The clinker thus obtained effectively controls the oc' currence of therapid expansion accompanied by the use of lime alone to cause a mild andprolonged expansion of a cement containing the clinker at the propertime during the progress of hardening of the cement. Hence, it is usedas a very effective inflating agent for cement.

DETAILED DESCRIPTION OF THE INVENTION As the lime used in this inventionas the main raw material, any material which can provide a CaO source,such as limestone, calcium oxide or calcium hydroxide, may be employed.

The ferric oxide used as one of the additives to the lime in thisinvention is mainly composed of Fe O and can contain impurities but itis necessary that such impurities be inactive toward lime. Inparticular, mill scale is preferably utilized as the ferric oxide. Also,the

' calcium fluoride and the calcium sulfate to be used as the additivesin this invention can contain impurities which are inactive toward lime.Generally, commercially available materials can be employed as suchadditives.

The amounts of ferric oxide, calcium fluoride, and calcium sulfate tothe lime will be explained by relating the amounts added in terms of CaOand to the expan sion effect of a mortar prepared by compounding theexpansive additive formed by sintering the mixture of lime and theadditives in a cement as shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph showing thecharacteristics concerning the expansion coefficient of a cement, havingadded thercto'a cement expansive additive containing lime and ferricoxide, with age.

FIG. 2 is a graph showing the characteristics concerning the expansioncoefficient of a cement having added thereto a cement expansive additivecontaining lime and calcium fluoride, with age.

FIG. 3 is a graph showing the characteristics concerning the expansioncoefficient of a cement, having added thereto a cement expansiveadditive containing lime and calcium sulfate, with age.

The cement expansive additive prepared by mixing a powdered limestonecrushed to a size smaller than 88 microns and a ferric oxide powder (FeO crushed into a size smaller than 88 microns in the weight ratio shownin the table below, heating the mixed powders in an electric mufflefurnace for 2 hours at temperatures of l,400-l,450C to provide aclinker, and crushing the clinker to a size smaller than 149 microns wascompounded in a cement in an amount of 6 percent by weight. The relationbetween the expansion characteristics of the cement and the curingperiod (in days) is shown in FIG. 1.

For comparison, calcium oxide (CaO), Prepared by baking the powder oflimestone for 1 hour at l,400C without added Fe O was added to a cementin an amount of 3 percent by weight and the relation of the expansioncharacteristics of the cement and the curing period is shown in FIG. 1as Curve F.

Also, the expansive additive prepared similarly by mixing powderedlimestone crushed smaller than 88 microns and powdered calcium fluoride(CaF crushed smaller than 88 microns in the weight ratio shown in thefollowing table, sintering the mixture by heating the mixture in anelectric muffle furnace under the same conditions as used for FIG. 1 toprovide a clinker, and crushing the clinker smaller than 149 microns wascompounded in a cement in an amount of 4 percent by weight. The relationof the expansion characteristics of the cement and the curing period indays is shown in FIG. 2. For comparison, the use of powdered calciumoxide alone is also shown in FIG. 2 as Curve Moreover, the expansiveadditive prepared by mixing powdered limestone crushed smaller than 88microns and powdered calcium sulfate (CaSO,) crushed smaller than 88microns in the mixing ratio shown in the table below, sintering themixture by heating it in an electric muffle furnace for 2 hours atl,200-l,300 C to provide a clinker, and crushing the clinker smallerthan 149 microns was compounded in a cement in an amount of 5 percent byweight. The relation between the expansion characteristics and thecuring period is shown in FIG. 3. For comparison, use of powderedcalcium oxide alone is shown in the same FIG. 3 as Curve The mortarsamples used above were prepared by the JIS K5201 method and theexpansion characteristics of the mortar were obtained by means ofcomparative measurements of the change of the surface length duringcuring in water at C using the smacelengtlrof sample justaftercoagulation and release of the mold as the basis.

As is clear from the results shown in FIGS. 1 to 3, the mortarcontaining calcium oxide alone with no expansion controlling agent suchas ferric oxide, calcium fluoride or calcium sulfate, suffered rapidexpansion at the beginning of aging, while the mortar containing calciumoxide together with ferric oxide, calcium fluoride or calcium sulfateexpanded gradually during aging, as shown by the slowly changing curve,and became stable after about 3 weeks.

The results obtained also show that the expansion characteristics of themortar are influenced by the amount of expansion controlling agent addedand an increase in the amount of the additive, results in a tendency forthe expansion of the mortar to occur later.

As far as the results shown in the graphs are concerned, the effect ofthe addition of ferric oxide, calcium fluoride or calcium sulfate, whichcontributes to the control of the expansion of the cement, is at amaximum in Curve E, J, or M respectively.

in this respect, further investigations were made into the effectiveamount of the aforesaid expansion controlling agent together with theminimum amount thereof capable of showing the expansion controllingeffect. It was discovered that the critical characteristics were shownby Curves R and S in FIG. 1, Curves T and U in FIG. 2, and Curves V andW in FIG. 3.

Accordingly, the effective amount of ferric oxide to be added is about340% by weight of the total weight of the sintered product, that ofcalcium fluoride is about 360% by weight, and that of calcium sulfate isabout 30-85% by weight. In particular, a preferred amount of ferricoxide is from 5 to 35% by weight, that of calcium fluoride is from 20 to50% by weight, and that of calcium sulfate is from 55 to by weight.

The mixture of limestone and the additive must be heated at temperatureshigher than 1,200C until the mixture becomes a homogeneous sinteredstate or semi-molten state. If the mixture is insufficiently sintered,the effect obtained with the sintered product is the same as thatobtained with calcium oxide alone in the expansion characteristics ofthe cement to which the clinker is added. In other words, no effect ofthe additive is obtained. Therefore, when the heating period forsintering the mixture is about 1 to 2 hours, the proper heatingtemperature is about 1,450C where ferric oxide is used as the additive,about l,400C where calcium fluoride or a mixture of ferric oxide andcalcium fluoride is used as the additive, and about l,200l ,300C wherecalcium sulfate is used as the additive.

In addition, the same experiments described above were repeated usingindustrial raw materials such as calcium oxide prepared by bakinglimestone, mill scale, fluoride, and gypsum by-products in theproduction of hydrofluoric acid instead of the limestone, ferric oxide,calcium fluoride, and calcium sulfate respectively. Almost the sameresults as described above were obtained.

The amount of the expansive additive in this invention to be compoundedwith the cement will be explained below.

An expansive additive generally shows different expansioncharacteristics with the passage of time depending on the compositionthereof. Also, when the composition of an expansive additive remainsconstant, the expansion characteristics thereof were, of course, higheras the amount of the agent to be compounded in cement is increased.Furthermore, since the proper compounding ratio of the expansiveadditive in this invention to cement necessary for causing an expansionof from 1 to 1.5%, by which the shrinkage of an ordinary cement can becompletely prevented, depends upon the composition of the expansiveadditive. It is generally impossible to define numerically thecompounding ratio thereof but it is usually preferable to add theexpansive additive to a cement in an amount of from about 3 to 10% byweight based on the weight of the cement. If the amount of the expansiveadditive is less than about 3% by weight, it cannot provide effectiveexpansion characterics. While, if the amount is larger than 6% byweight, the mechanical strength of the cement after setting is reduced.For example, the most preferred compounding ratio of the expansiveadditive is about 6% by weight when the ratio of the calcium oxide tothe ferric oxide of the inflating agent is :15, about 4% by weight whenthe ratio of the calcium oxide to the calcium fluoride is 70:30, about5% by weight when the ratios of the calcium oxide to the ferric oxide tothe calcium fluoride are 70:15:15, and about 6% by weight when the ratioof the calcium oxide to the calcium sulfate is 45:55.

The invention has been described in terms of blending of mortar but isalso applicable to the blending of concrete.

From the above descriptions it will be understood that in the presentinvention, ferric oxide, calcium fluoride, and calcium sulfate exhibitan effective and a similar function for controlling the expansioncharacteristics of calcium oxide to cement when they are employedindividually or in combination together with calcium oxide.

This invention will be explained further by reference to the followingexamples.

EXAMPLE 1 A mixture of 91 parts by weight of limestone having a purityof 98% and 9 parts by weight of mill scale was crushed and baked for 2hours at l,450C to provide a clinker for use as an expansive additive.The clinker was crushed and added to a cement in an amount of 5% byweight or 6% by weight to provide cement or and cement [3, respectively.For comparison, a conventional cement containing no such expansiveadditive was prepared.

By using the cement prepared above a 10 X 10 X 50 cm concrete sample wasprepared. The composition of the concrete per cubic meter thereof was asfollows:

Blend Blend 0 Blend 5 Expansive Additive of this Invention l68 kg 19] kgOrdinary Portland Cement 299 kg 296 kg Water 218 kg 218 kg Gravel (2.5mm in diameter) 955 kg 955 kg Sand 876 kg 876 kg Total 2364 kg 2364 kgThe expansion coefficient of the concrete during curing in water at 20C,measured by the above-described method employed with the mortar samples,is shown in the following Table 1.

A powdered mixture of 70 parts by weight of calcium oxide prepared bybaking limestones at 1,200C and 30 parts by weight of fluoride washeated for 2 hours at l,400C to provide a clinker as an expansiveadditive. The clinker was crushed smaller than 149 microns andcompounded in a cement in an amount of 4% by weight to provide cement y.

Separately, a powdered mixture of 70 parts by weight of calcium oxide,parts by weight of mill scale, and 15 parts by weight of fluoride washeated for 2 hours at 1,400C to provide a clinker as an expansiveadditive. The clinker was crushed into a size smaller than 149 micronsin diameter and compounded in a cement in an amount of 5% by weight toprovide cement 8.

The expansion coefficients of the cements prepared above were measuredby the same test procedure as used in Example l and the results areshown in Table TABLE 2 Expansion Coefficient (x l0 5) Type Age (day)Cement 8 I22 EXAMPLE 3 A powdered mixture of calcium oxide having apurity of 98 percent and a gypsum by-product obtained in the productionof hydrofluoric acid and having a purity of 90 percent mixed in a weightratio of 40:60 or 20:80 and was baked for 2 hours at l,200C to provide aclinker as an expansive additive. The clinker was crushed to smallerthan 149 microns and was added to a cement in an amount of 5 percent byweight in the former (40:60 mixture) and 8 percent by weight in thelatter (20:80 mixture) to provide cement e and cement 6.

The expansion coefficients of these cements were measured by the sametest method as used in Example I and are shown in the following table.

What is claimed is:

l. A cement composition consisting essentially of a cement and from 3 to10 percent by weight of a crushed sintered mixture of lime and at leastone additive selected from the group consisting of ferric oxide, calciumfluoride and calcium sulfate, said crushed sintered mixture beingobtained by heating said mixture to a temperature of from about 1,200 toabout 1,400C for from about 1 to 2 hours followed by cooling andcrushing.

2. The cement composition of claim I, wherein said additive is ferricoxide and said ferric oxide is present at a level of from 3 to 40percent by weight based on the weight of the crushed sintered mixture.

additive is calcium sulfate and said calcium sulfate is present at alevel of from 30 to by weight based on the weight of the crushedsintered mixture.

2. The cement composition of claim 1, wherein said additive is ferricoxide and said ferric oxide is present at a level of from 3 to 40percent by weight based on the weight of the crushed sintered mixture.3. The cement composition of claim 1, wherein said additive is calciumfluoride and said calcium fluoride is present at a level of from 3 to60% by weight based on the weight of the crushed sintered mixture. 4.The cement composition of claim 1, wherein said additive is calciumsulfate and said calcium sulfate is present at a level of from 30 to 85%by weight based on the weight of the crushed sintered mixture.